Thanks to ccoli and toolittletime from this board (and a very pleasant trip to Idaho a couple of months back), I have in my posession an early UNIT brand leading link front suspension. If you're not familiar with the Leading Link front suspension concept, think "traditional rear swing arm suspension pointed forward". I've wanted a LL since I started designing the trike, but couldn't find a donor for the project. So until now I've been running traditional tele-forks with a 7ยบ rake on the trees. The raked trees were an improvement over the regular EV geometry, but still left something to be desired in terms of optimal trail, ease of steering, better braking, and better dive control under decel and braking.
Over email and the phone Chris explained that he'd come across a possible donor for my Leading Link Lust. Mostly I think he was protecting his own front end from pillferage, on account of every time I saw his I warned him that it could come up missing some day. Chris said the UNIT setup came with the basic forks, swing arm, shocks, trees, brakes, wheel, and axle intended to fit what we assume was a K-bike. It had been loosely (and I mean that literally) adapted to some manner of Guzzi, since it had the stick bird logo on some flavor of 40mm oem triple clamps. It was however way too narrow to fit my front Lester mag. It also had parts that had been modified to no apparent purpose. It would need to come apart and get a major workover, which appealed to my sense of humor. I said I'd go for it.
Chris and his charming wife, Judy, were headed from Wisconson to Alaska, on a combination ferry ride and sidecar adventure. I was in western Washington, which put me on their travel path. However, they couldn't carry all those shoes AND the leading Link stuff on the hack. But they were trailering to north Idaho, so we arranged for a handoff there. As fate has it, I live at the far western end of highway 20, a legendary motorcycle byway. They would be at the Idaho end. So my choice of route was a no-brainer. Any day you can do the entire Washington section of highway 20 is a good day.Taking it both directions is even better, even in a Jeep.
Once I got it back to the ranch I sorted and and dimensioned everything. Yes, it was too narrow, but there was only one point that needed splicing to widen it. The fork tubes had less diameter than my triple clamp bores, but there was a catalog bushing to make the fit. The axle was also diameter impaired, but again there were standard bushings to bring it to size. Once they arrived I was ready to go to work.
I mocked up the swing arm geometry I needed and took the trees, forks, axles, and attending stuff to a weld shop to be widened. It was expensive, but I wanted a certifiable weld at that point. While I was waiting on them I removed the trike's existing front end.
The build was really unremarkable. I assembled the headstock, placed the bushings on the fork tubes, and ran the tubes smoothly through the clamps.
I left the pinch bolts loose to help align the swing arm bushings, and a little wiggling was all it took to pop the swing arm into place. I got the pivot bolts installed (replaced later for length) and the pinch bolts secured the forks in their clamps.
I have a couple sets of shocks. The length of the shock and its spring rate set up the swing arm angle. I started with the long set. So far so good -- everything slips or snicks into place like assembling a firearm: positive feedback from each part as it is added. Everything seems parallel, perpendicular, or whatever is correct. With proper sized fasteners everything should become tight and still articulate. With the components at ride height, trail is -2.5" -- about as tight as I want it.
When I added the wheel I didn't like the brake setup as I could see it developing. The early UNIT LLs had a pair of Brembos with four 25mm pistons per unit, rigidly mounted below the swing arm and behind the axle. They were positioned for some wheel other than a Lester, and some brake rotors with a different offset than mine. In addition, I wanted to run 320mm rotors, and the welded lugs for mounting the Bremos were set up for a 280mm disk. Given the shortcomings of the rigid mount and the awkward shape of the necessary spacer, I decided to abandon that concept altogether and "float" the calipers. In standard automotive terms, a floating caliper is one with pistons on one side only, that "floats" on pins to center the caliper on the rotor. This is different from our traditional Brembos, which have pistons in both sides, are rigidly mounted and shimmed to center on the rotor.
In sidecar and trike jargon, floating the calipers means that they are attached to a mount that swings freely (floats) radially around the axle and is also free to move along the axle axis as well. Think connecting rod on a crankshaft. Hmm. Come to think of it, I could have used con rods. That would have been a cool touch. Floating the calipers is a more complicated way to build a brake, but it has advantages for the trike (eventually explained below).
I chose a pair of Tokico twin-30mm-pot radial mount calipers from a gsxr simply because they were in the size range I needed and the radial mount seemed easier to fabricate. I'm pumping them with a 3/4" Nissin radial master cylinder, and went with braided teflon hoses.
The first job was to center the wheel in the swing arm. I removed it from the forks for ease of work. Since the Guzzi axle sets up with spacers, this was not a big chore -- I just added and subtracted shims until it was right, measured the distances, and made a single piece spacer with a 19mm ID and 25mm OD for each side. When the axle nut is drawn up tight, the spacers and bearing races create a solid wheel center.
Then I made the floating mounts. With the radial calipers, the mounts could be simple 3/16 angle irons fitted with bushings at the axle end.
The bushings were reamed to fit over those axle spacers I described above so they moved freely around and along the axle, with no discernable wobble.
I found the distance from the axle center to the mounting base of the calipers and sized the mounting brackets. I bored the axle ends for the shaft collars and cut perches for the calipers. When I found the proper point of axial float that didn't hang up in the wheel or bind the calipers, I welded the shaft collars and perches into place.
A caliper that floats doesn't work if it just keeps spinning with the rotor when applied, so it needs a strut to hold it in place. Think torque rod on a loop frame rear drum. The strut needs to be wobbly enough to move with the centering and axial float of the caliper, but rigid in the push-pull directions. It also needs to be anchored at the fork's down tube rather than the swingarm, or you just have a rigid mount with a strut. And while all that is happening, the struts can't get in the way of anything else, like the fender, caliper, shock, or spokes.
I decided 3/8" turnbuckles would be sturdy and adjustable struts. I cut the eye ends off and replaced them with heim joints, which I screwed onto the shafts and then tack welded. With one end of the turnbuckle at the forward caliper mount, and the other at the top shock mount, I had the struts I needed. That completed the mechanical part of the brakes.
In a perfect world, a floating brake's turnbuckle struts would be parallel to the swing arm. If parallel, then the braking force is perpedicular to the fork leg, and the front end neither rises nor plunges under braking. In reality, mine are a little above that point, so it's a little over-centered and there's a little bit of plunge as the shocks and springs absorb some of the force (if the anchor was lower than parallel, the front end would rise). So the more parallel the geometry, the more braking force goes to stopping the trike instead of loading up the suspension. I like that part.
The hydraulic part of the brakes turns out to be complicated too. I was sad with the initial results -- the hoses I had on hand were the wrong sizes for a tidy install, and the pump faded. Too much brake fluid later, I ordered in better sized hoses and a rebuild kit for the master cylinder. Still not happy, I ordered and added a 2# residual check valve between the pump and the front brake splitter. Now I had an awkward bend in the hose that seemed to be an air trap, but no Russell banjos on hand to improve the angles with. Still working on that, but if I hang the calipers from a ladder higher than the pump, I can get the air. A real PITA.
With the brake components in place, I set about mounting the fender. After centering it up with turnbuckles and a small jack I puzzled out a permanent mounting scheme.
The donor LL had come with an ugly hoop bracket, and if I worked on the tabs I could make the angles for the front mount. The rears were problematic. The fender ended up just too much in one direction or some other to use simple bracketry. I had to weld tabs to the swing arm strut and bracket off of them. But I think I got the fender and wheel arcs about where I want them.
The work came to an abrupt end. I straightened up from the unteenth reassembly of every darn bit and realized that everything was sanded, centered, lubed, torqued, bled, measured, washed, tested, and even slept over. Nothing bound, squeaked, leaked, or clicked. The fairing was even repositioned and all wires accounted for. I was suddenly without excuses to not drive it.
I made my first few runs down a closed road after dark, which allowed me to dial in the headlights and check the broad strokes of steering, suspension, and brakes. The road is closed because after a couple of blocks it lookes like a bombed runway. A bike could literally disappear in the craters. I negotiated them under headlights with no problems -- steering was nimble, brakes did their job, and I bottomed out neither the engine nor the shocks.
The brakes sucked. They always do. But nothing snagged or rattled or shook, and most importantly, nothing fell off, got out of control, or failed to function. I hate it when that happens. I brought it back to the garage and found more air in the brakes. I'd been having problems with the Wilwood 2# pressure valve joints leaking. I JB-quicked it.
In the daylight, between rain showers, I put about 30 miles on it in twisties, town traffic, and the highway, taking it as high as 60mph, but mostly in the 40 - 55mph range. Nothing snagged or rattled or shook, and most importantly, nothing fell off, failed to function, or got out of control. I hate it when that happens enough to say so again.
The turning radius hasn't changed, but the way it handles irregular surfaces has. I now have a wheel of choice for hitting most potholes and small animals. With the swing arm pushing the wheel from a few degrees under horizontal instead of the near vertical plunge angle of teleforks, and the top shock mount anchored to the lower part of the tube, it wants to roll over obstacles like a wheelbarrow rather than a shopping cart. So the front wheel rises or drops without transferring much motion or shock up through the handlebar.
It tracks very differently. As long as I'm not moving the bar, it wants to go straight. But the handlebar is very easy to move, and when I move it even a twitch, the course change is immediate -- almost an oversteer at shallow angles. The front wheel goes easily where I point it at up to 20-over on some posted curve speeds, and the rear end follows right behind it without the "yawing" feeling I had previously. So I think I got the trail, ride height, and shock/spring rates about right. It does have a little bit of headshake if I take my hands off the bars, and there might be a little bit of throbbing -- maybe from a slightly dragging brake. I have a steering damper and expected to use it. The harmonic throb though I have not identified.
The rain has started and might continue for the winter. I'm waiting for a break in it (Tuesday, maybe?) to test the new brake pads and steering damper. I'll play with tire pressures too -- always looking for that sweet spot where comfort and handling meet. I'm also working with Beetle on the fuel map. I've got an additional couple hundred or so miles on it since I wrote down my first impressions. I'm finding one major problem with the front end overall, especially when trying to get out of parking spots and gas lanes: It collects crowds like the windscreen collects bugs.
And that's your report. Goodnight!
